Beetle solves photonic-crystal mystery that's bugged researchers

PORTLAND, Ore.  Semiconductor makers should take a hint from Mother Nature when pursuing photonic crystals for optical computing, according to University of Utah researchers studying the Brazilian beetle: this bug's eerie iridescence is evidence of its unique photonic lattice structure--called the "champion" architecture in photonic circles.

Diamonds have it, but they cannot act as photonic crystals because their atoms are packed too tightly together. By replacing the diamond's carbon atoms with cylindrically shaped molecules spaced to match a single wavelength of light, the beetle's scales could hold the key to solving long-standing problems with fabricating three-dimensional diffraction gratings within photonic crystals.

"We are currently utilizing the knowledge we discovered by studying the beetle's scales, and are now finding a way to make the same structure in a much more relevant material--an inorganic semiconductor--about which we hope to announce details later this summer," said University of Utah professor, Michael Bartl.

Since the 1990s, when photonic crystals were most recently popularized, the ideal, or "champion," architecture has been sought for the filtering ability of its band-gap, which depends on the spacing between nodes in a lattice. Just as silicon's band-gap enables transistors to perform not just data-communication tasks, but also amplification and computation, likewise photonic crystals with band gaps should be able to amplify and compute with light instead of electrons. Photonic crystals can also make solar cells more efficient, directing specific wavelengths of light to catalyze chemical reactions, and ultimately enable the fabrication of on-chip lasers for all-optical chips.

Unfortunately, the illusive photonic crystal semiconductor has been easier to imagine than to actually construct. One- and two-dimensional photonic crystalline-like architectures have been fabricated with planar chipprocessing steps, but three dimensional (3D) photonic crystals required tedious construction methods that have so far met with limited success.

Now these University of Utah researchers claim to have found a better method by following the example of nature--the iridescent green scales of an inch-long weevil named Lamprocyphus augustus. By dissecting its scales into more than 150 cross-sections, each recorded with an electron microscope, the researchers discovered the secret of its construction technique, and claim to be currently realizing that structure in a semiconductor.